Laws of Motion Test

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Laws of Motion Test - 43

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Weekly Quiz Competition

Question 1
1 / -0

While dusting a carpet, we give it a sudden jerk or beat it with a stick because:

A
the inertia of rest keeps the dust in its position and the dust is removed when the carpet moves away.

B
the inertia of motion removes dust.

C
no inertia involved in process.

D
jerk compensates for the force of adhesion between dust and carpet and dust is removed.

Solution

While dusting we give a sudden serk our beat with stick because when we do that stick because when we do that the particle of carpet move with our help and the dust particle stays at rest by inertia and eventually they separate from the carpet.
Question 2
1 / -0

A pushing force acts on the trolley as shown. Which arrow shows the frictional force acting on the wheel X?

A
A

B
B

C
C

D
D

Solution

As w.k.t friction always oppose the motion.

Hence, cart move right then friction act on wheel left along -B
Question 3
1 / -0

A cricket ball of mass 500 g is moving with speed of $$36 \,km\,h^{-1}$$. It is reflected back with the same speed. What is the impulse applied on it?

A
20 Kg m/s

B
10 Kg m/s

C
5 Kg m/s

D
none of the above

Solution

Impulse $$I=$$ change in momentum $$=mv_2-mv_1$$
Here, $$v_1=-v_2=36 km/h$$
So, $$I=(500/1000)[-36-36]=-36 kg.m/s$$
The magnitude of impulse $$=36 kg.m/s$$
Question 4
1 / -0

A cricket ball of mass 120 g is moving with a velocity of 12 m $$s^{-1}$$. It turns back and moves with a velocity of 20 m $$s^{-1}$$ when hit by a bat. Find the impulse if the force acts on the ball for 0.02 s.

A
4 N s

B
8 N s

C
32 N s

D
192 N s

Solution

Initial velocity of ball $$u = -12 \ m/s$$
Final velocity of ball   $$v = 20 \ m/s$$
Magnitude of change in momentum   $$|\Delta P| = m (v-u) = 0.12\times (20-(-12)) =3.84 \ kg \ m/s $$
Time of action $$\Delta t = 0.02 \ s$$
Thus impulsive force   $$F = \dfrac{\Delta P}{\Delta t} = \dfrac{3.84}{0.02} = 192 \ N$$
Question 5
1 / -0

A $$1\ m$$ long uniform beam is balanced as shown. Calculate the force F.

A
$$2\ N$$

B
$$3\ N$$

C
$$7\ N$$

D
$$11\ N$$

Solution

Moment of force $$ M=$$ force $$\times $$ perpendicular distance from pivot
For the balanced beam, the net moment of force on left side of pivot is equal to the net moment of force on right side.
Thus, $$5N(50-10 )cm= F(60 -50) cm+ (3N)(80-50)cm$$
or $$20=F+9$$ or $$F=11 N$$
Question 6
1 / -0

Momentum is a measure of quantity of _______.

A
motion

B
friction

C
gravitation

D
electric force

Solution

Momentum is a measure of the quantity of motion possessed by an object by virtue of its mass and velocity. Massive objects have high momentum than lighter objects and fast-moving objects have high momentum than slow moving objects.
So, option $$A$$ is the correct answer.
Question 7
1 / -0

A hammer of mass 5 kg moving with a speed of $$2ms^{−1}$$ strikes the head of a nail driving it 20 cm into the wall. Find the impulse(in N s).

A
0

B
-100

C
-10

D
-10000

Solution

Impulse = change in momentum

Impulse = final momentum - initial momentum

                 = $$0$$ - $$(5kg\times 2ms^{-1})$$

                = $$-10kgms^{-1}$$

                 = $$-10Ns^{-1}$$
Question 8
1 / -0

When a body is stationary, then:

A
there is no force acting on it.

B
the body is in vacuum.

C
the forces acting on it are not in contact with it.

D
the net forces acting on it balance each other.

Solution

If the net external force acting on the body is zero, the body either remains at rest or move with constant velocity. Hence, if the given body is stationary, the net forces acting on it balance each other.
Question 9
1 / -0

The time, in which a force of 2 N produces a change in momentum of $$0.4\, kg\, m\, s^{-1}$$ in a body whose mass is 1 kg is:

A
0.2 s

B
0.02 s

C
0.5 s

D
0.05 s

Solution

Impulse $$I=Ft$$
also $$I=$$change in momentum $$=0.4 kg m/s$$
So, $$0.4=(2)t $$ or $$t=0.2 s$$
Question 10
1 / -0

The impulse of a body is equal to:

A
Rate of change of its momentum.

B
Change in its momentum.

C
The product of force applied on it and the time of application of the force.

D
Both (B) and (C)

Solution

Impulse $$I=Fdt$$
Also force $$F=m\dfrac{dv}{dt}$$
So, $$I=m\dfrac{dv}{dt}dt=mdv=m(v_2-v_1)=mv_2-mv_1=p_2-p_1=$$ change in momentum
Thus, both B and C are correct.

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Re-Attempt Weekly Quiz Competition

Laws of Motion Test - 43

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Laws of Motion Test - 43

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SHARING IS CARING

Question 1

the inertia of rest keeps the dust in its position and the dust is removed when the carpet moves away.

the inertia of motion removes dust.

no inertia involved in process.

jerk compensates for the force of adhesion between dust and carpet and dust is removed.

Solution

Question 2

A

B

C

D

Solution

Question 3

20 Kg m/s

10 Kg m/s

5 Kg m/s

none of the above

Solution

Question 4

4 N s

8 N s

32 N s

192 N s

Solution

Question 5

$$2\ N$$

$$3\ N$$

$$7\ N$$

$$11\ N$$

Solution

Question 6

motion

friction

gravitation

electric force

Solution

Question 7

0

-100

-10

-10000

Solution

Question 8

there is no force acting on it.

the body is in vacuum.

the forces acting on it are not in contact with it.

the net forces acting on it balance each other.

Solution

Question 9

0.2 s

0.02 s

0.5 s

0.05 s

Solution

Question 10

Rate of change of its momentum.

Change in its momentum.

The product of force applied on it and the time of application of the force.

Both (B) and (C)

Solution

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